In the related art, most of portable electronic devices are supplied with power for operation from a battery. However, a volume and a weight of the portable electronic device are increased because a battery is mounted in the portable electronic device, and a user is inconvenienced because the battery is recharged due to a restricted power supply of the battery.
A technology for solving the problems is a wireless power transmission method. The wireless power transmission method includes a power transmitting device which supplies electrical energy, and a power receiving device which receives the supplied electrical energy and charges the battery.
One of the most widely used wireless power transmission technology is an inductive coupling method. The inductive coupling method enables the user to easily charge an electronic device such as a portable device because electrical signals generated at transmitting and receiving sides are transmitted in a wireless manner through a coil. Recently, a wireless power transmission technology, which has a high efficiency and exceeds an appropriate radio wave range by using a pair of inductively coupled resonant coils having a high Q factor, has been developed.
A resonant coupling method refers to a method that uses a receiving coil configured as an LC resonator, and a transmitting coil. In this case, both of the receiving coil and the transmitting coil are adjusted to have the same or similar resonant frequency. With the resonance phenomenon, the wireless power transmission technology may transmit power even though the transmitting coil and the receiving coil have a small coupling coefficient or the transmitting coil and the receiving coil are positioned far away from each other.
However, there are problems in that transmission efficiency of the wireless power transmission method is not high in comparison with other power supply methods, and the transmission efficiency depends on various environmental factors. Therefore, there is a need for improved power transmitting and receiving devices for improving power transmission efficiency of a wireless power transmission apparatus.